Recombinant Mouse Transmembrane protein 201 (Tmem201)

What is Tmem201 and what is its cellular localization?

Tmem201 is an integral inner nuclear membrane (INM) protein found in the nuclear envelope. It is specifically localized to the INM, which forms part of the nuclear envelope along with the outer nuclear membrane and nucleopore . The protein contains approximately 664 amino acids in mouse (full-length protein) and has several transmembrane segments that anchor it to the nuclear envelope . Tmem201 is also known by several aliases including Samp1, AV028368, D4Ertd429, Net5, Sa, and D4Ertd429e, which reflects its discovery through different research approaches .

To detect and analyze Tmem201 localization in experimental settings, researchers typically utilize immunofluorescence techniques with tagged versions of the protein (such as TMEM201-flag) due to limitations with direct antibody detection. Colocalization studies have demonstrated that Tmem201 positions in close proximity to other nuclear envelope components including SUN2 and LaminA/C .

What is the structural organization of Tmem201?

Tmem201 is a multi-domain transmembrane protein with a complex structural organization:

• The protein contains five predicted transmembrane segments (TMSs)

• The N-terminus and C-terminus before the last TMS are exposed in the nucleoplasm

• The N-terminus contains a highly conserved Ima1 N-terminal domain with eight conserved cysteines organized as four CxxC motifs, predicted to form two zinc fingers

• The zinc finger motifs appear critical for proper INM localization of TMEM201

When designing experiments to investigate Tmem201 function, it's important to consider these structural features, particularly when creating truncation mutants or fusion proteins. The N-terminal domain has been shown to be particularly significant for protein interactions and function, while artificial constructs lacking this domain fail to rescue functional deficits in knockout models .

What methods are available for generating recombinant Tmem201 for experimental use?

Recombinant Mouse Tmem201 is available commercially as a full-length protein (1-664aa) with greater than 85% purity as determined by SDS-PAGE . For experimental purposes, researchers can also generate their own recombinant Tmem201 using:

• Cell-free expression systems, which have been successfully employed to produce functional recombinant protein

• Mammalian expression vectors with epitope tags (such as flag or myc) for detection purposes

• Truncation constructs targeting specific domains (N-terminus or C-terminus) to investigate domain-specific functions

For co-immunoprecipitation experiments, TMEM201-flag constructs have been successfully used to detect interactions with binding partners such as SUN2-myc and LaminA/C .

What are the known cellular functions of Tmem201?

Tmem201 has been implicated in several critical cellular processes:

• Nuclear envelope structure: As an INM protein, Tmem201 contributes to nuclear envelope integrity and organization

• Cell migration: Tmem201 positively regulates cell motility across multiple cell types:

  • In endothelial cells, TMEM201 depletion impairs migration in transwell and wound healing assays

  • In fibroblasts, a variant of TMEM201 (Samp1) positively regulates nuclear movement during polarization and migration

  • In breast cancer cells, TMEM201 promotes migration and invasion

• Angiogenesis: TMEM201 is required for endothelial cell angiogenic behavior, including:

  • Tube formation (>50% reduction in junctions and branches observed in knockdown cells)

  • Sprouting in fibrin gel bead assays

  • Endothelial cell polarity establishment (reduced Golgi apparatus reorientation in TMEM201-deficient cells)

• Signal transduction: TMEM201 participates in specific signaling pathways:

  • In breast cancer, it physically interacts with SMAD2/3 and regulates TGFβ signaling

  • In endothelial cells, it interacts with the LINC complex to regulate migration

How does Tmem201 interact with the LINC complex and what is the functional significance?

Tmem201 physically interacts with components of the linker of nucleoskeleton and cytoskeleton (LINC) complex, which is crucial for connecting the nuclear envelope to the cytoskeleton and facilitating nuclear positioning during cell migration . Key findings include:

• Colocalization analysis shows potential direct interaction between TMEM201 and SUN2, as well as LaminA/C, in endothelial cells

• Co-immunoprecipitation assays confirm these interactions: TMEM201-flag can pull down SUN2-myc and LaminA/C, and vice versa

• The N-terminus of TMEM201 specifically interacts with the LINC complex, while truncation mutants lacking the N-terminus (TMEM201△N) fail to pull down LINC components

• Functionally, expressing full-length TMEM201-flag accelerates endothelial cell migration and angiogenesis, while expressing TMEM201△N-flag fails to promote these processes

This interaction appears crucial for TMEM201's role in regulating cell migration, as disruption of the LINC complex impairs cell motility and angiogenesis .

What phenotypes are observed in Tmem201 knockout/knockdown models?

Experimental manipulation of Tmem201 expression levels has revealed significant phenotypes across different model systems:

In vitro models:

• TMEM201 knockdown in human umbilical vein endothelial cells (HUVECs) via shRNA results in:

  • Impaired tube formation with >50% fewer junctions and branches

  • Decreased migration in transwell and wound healing assays

  • Reduced Golgi apparatus reorientation (polarity establishment)

  • Slightly inhibited proliferation rate

Mouse models:

• Tmem201-knockout mice (generated by CRISPR/Cas9) are viable but show:

  • Reduced extension of the superficial vascular plexus in retinas at postnatal day 6

  • Impaired vessel outgrowth and branching from aortic rings

Zebrafish models:

• tmem201 deletion mutant zebrafish exhibit:

  • Defective intersegmental vessel (ISV) development

  • This phenotype can be rescued by expressing wild-type tmem201 but not by tmem201△N-terminus, highlighting the importance of the N-terminal domain

How does Tmem201 contribute to pathological conditions like cancer?

Tmem201 has been implicated in cancer progression, particularly in breast cancer:

• TMEM201 expression is significantly elevated in invasive breast cancer and predicts poor prognosis

• It functions as a positive modulator of breast cancer cell migration and invasion both in vitro and in vivo

• Mechanistically, TMEM201 deficiency inhibits epithelial-to-mesenchymal transition (EMT) and transforming growth factor-β (TGFβ) signaling

• TMEM201 physically interacts with SMAD2/3 and is required for:

  • SMAD2/3 phosphorylation

  • Nuclear translocation

  • Transcriptional activation of TGFβ target genes

These findings suggest that TMEM201 represents a potential therapeutic target in breast cancer, highlighting how specific inner nuclear membrane components can mediate signal-dependent transcriptional effects to control cancer metastasis .

What signaling pathways are affected by Tmem201 modulation?

Research has identified several signaling pathways that are influenced by Tmem201:

• LINC complex signaling: TMEM201 interacts with the LINC complex to regulate endothelial cell migration and angiogenesis . This interaction appears critical for establishing proper cellular polarity and directional migration.

• TGFβ-SMAD signaling: In breast cancer cells, TMEM201:

  • Physically interacts with SMAD2/3

  • Is required for SMAD2/3 phosphorylation

  • Facilitates nuclear translocation of phosphorylated SMAD2/3

  • Enables transcriptional activation of TGFβ target genes

• EMT regulation: TMEM201 deficiency inhibits epithelial-to-mesenchymal transition in breast cancer cells , suggesting its involvement in regulating cell plasticity and invasiveness.

Interestingly, TMEM201 deficiency does not appear to affect VEGF signaling in endothelial cells , indicating specificity in its signaling interactions.

What experimental approaches are most effective for studying Tmem201 function?

Based on successful approaches documented in the literature, the following experimental methods are recommended for investigating Tmem201 function:

Genetic manipulation:

• shRNA-mediated knockdown for in vitro studies

• CRISPR/Cas9-mediated knockout for generating animal models (mice and zebrafish)

• Expression of tagged constructs (TMEM201-flag, TMEM201-myc) for localization and interaction studies

• Domain truncation constructs to investigate structure-function relationships

Functional assays:

• Migration assays: transwell and wound healing assays

• Angiogenesis assays: tube formation, fibrin gel bead sprouting, competitive sprouting

• Polarity assessment: Golgi apparatus reorientation analysis

• In vivo models: retinal vessel development in mice, aortic ring sprouting, zebrafish intersegmental vessel development

Molecular interaction studies:

• Co-immunoprecipitation to identify protein-protein interactions

• Immunofluorescence confocal studies for colocalization analysis

• RNA-sequencing to identify transcriptional changes following TMEM201 manipulation

What are the common challenges in working with recombinant Tmem201?

Researchers should be aware of several technical challenges when working with Tmem201:

• Antibody limitations: The research-grade TMEM201 antibody may be incapable of direct immunofluorescence detection, necessitating the expression of tagged versions (e.g., TMEM201-flag) for localization studies .

• Transmembrane protein expression: As a multi-pass transmembrane protein, expression and purification of functional recombinant TMEM201 can be challenging. Cell-free expression systems have been used successfully .

• Functional redundancy: When designing knockout experiments, researchers should consider potential functional redundancy with other inner nuclear membrane proteins, as approximately 60 INM proteins have been identified .

• Domain specificity: The N-terminal domain appears critical for TMEM201 function, while the role of the C-terminal domain may vary between different model systems . This should be considered when designing truncation constructs.

How can Tmem201 research inform broader understanding of nuclear envelope biology?

Tmem201 research contributes to the broader understanding of nuclear envelope biology in several ways:

• While approximately 60 INM proteins have been identified, only a few have been well-characterized . Tmem201 studies provide insights into how specific INM proteins contribute to nuclear envelope function.

• The interactions between Tmem201 and the LINC complex elucidate mechanisms by which the nuclear envelope communicates with the cytoskeleton to regulate cell migration .

• The role of Tmem201 in TGFβ signaling in breast cancer cells demonstrates how INM proteins can directly participate in signal transduction and transcriptional regulation .

• Understanding Tmem201 function provides insights into the pathological consequences of nuclear envelope dysfunction, which has been implicated in various diseases including cancer and laminopathies.

What are the most promising future research areas for Tmem201?

Several promising directions for future Tmem201 research include:

• Detailed structural characterization: Elucidating the three-dimensional structure of TMEM201, particularly its N-terminal zinc finger domains, would provide insights into its interaction mechanisms.

• Tissue-specific functions: Investigating TMEM201 functions in different tissues beyond endothelial cells and breast cancer cells could reveal additional physiological roles.

• Therapeutic targeting: Exploring TMEM201 as a potential therapeutic target in cancer, particularly in breast cancer where it promotes invasion and metastasis .

• Developmental roles: Further characterization of TMEM201's roles in embryonic development, building on the zebrafish and mouse models .

• Transcriptional regulation: Investigating how TMEM201 influences gene expression patterns, potentially through its interactions with nuclear envelope components and signaling factors.

What methodological improvements would advance Tmem201 research?

Advancements in the following methodological areas would significantly enhance Tmem201 research:

• Improved antibodies and detection methods: Development of high-quality antibodies capable of detecting endogenous TMEM201 in immunofluorescence applications.

• Live cell imaging techniques: Methods to visualize TMEM201 dynamics during cell migration and division in real-time.

• Domain-specific interaction mapping: More precise identification of which TMEM201 residues interact with specific binding partners.

• Conditional knockout models: Development of tissue-specific and inducible Tmem201 knockout models to overcome potential developmental defects in constitutive knockouts.

• Proteomics approaches: Comprehensive identification of the TMEM201 interactome under different cellular conditions and in various cell types.